6SN7GTA NOS SYLVANIA Chrome Top Matched Pair - Same Production Code - Low Noise & Microphonics - AMPLITREX Tested

6SN7GTA NOS SYLVANIA – Short Base Chrome Top – Matched Pair – Same Data Codes – Made in USA 1955 AMPLITREX Tested – VERY STRONG – Green Dot & Gray Dot – Low Noise & Microphonics Test Results: Tubes tested on an Amplitrex AT-1000 Tube Tester: Test Conditions: Va = 250V, Vg = -8V Average 100% Gm = 2600 ; Ia = 9.0 mA Test Result: VERY STRONG Tube #31 Section 1: Gm = 2600 ; Ia = 8.0 mA Section 2: Gm = 2600 ; Ia = 7.8 mA Tube #1 Section 1: Gm = 2600 ; Ia = 8.0 mA Section 2: Gm = 2680 ; Ia = 9.0 mA Additional Tests: Burn-in / Stability Test: 48h – OK Microphonics and noise: Very Low. Tested and suitable for use in hi-fi equipment and guitar amplifiers, including the most sensitive audio stages. Balance: Very Good. The sections are consistent and well-matched, making the tube suitable for use as a phase inverter in hi-fi and instrument applications. Emission: Excellent – Very strong and stable emission, without fluctuations. Short Circuits / Gas: none Description Exceptional NOS pair of 6SN7GTA Sylvania, manufactured in the United States in 1955 and carefully selected as a Matched Pair. Both tubes share the identical manufacturing code 288 / 513, dating back to the 13th week of 1955, and feature the characteristic Short Base Chrome Top construction. A particularly interesting combination for those seeking original American-made Sylvania tubes from the 1950s, with documented construction identity and manufacturing origin. The measurements performed with an Amplitrex AT-1000 highlight a particularly accurate match. The transconductance of the four sections ranges from 2600 to 2680 µmhos, with averages of 2600 and 2640 µmhos for the two tubes, perfectly in line with or above the nominal reference of 2600. The anode currents range from 7.8 to 9.0 mA, with averages of 7.9 and 8.5 mA, respectively. The remarkable uniformity of the transconductance, accompanied by a good current balance, confirms the quality of the match and the electrical consistency of the pair. Both tubes passed 48 hours of burn-in and stability testing, demonstrating very strong and constant emission, without fluctuations, short circuits, or gas. Noise and microphonics checks yielded very low results, allowing for the special Green Dot and Gray Dot classification. A particularly significant selection for audiophiles seeking reliable tubes even in the most sensitive amplification stages. The 6SN7GTA Sylvania tubes are appreciated for use in hi-fi preamplifiers, headphone amplifiers, driver stages, and compatible phase inverter circuits. Sylvania production from this period is traditionally sought after by enthusiasts for a musical reproduction generally described as natural, airy, and well-articulated, capable of combining definition and listening pleasure. The same production week in March 1955, the excellent preservation of the original markings, and the particularly well-maintained cosmetic condition complete the value of this pair. Two authentic vintage NOS Sylvania tubes, united by their manufacturing origin and selected to offer uniform electrical characteristics, verified stability, and extremely low noise: a choice of particular interest for those who wish to enhance their audio system with original American tubes from the 1950s. Condition Condition: NOS - New Old Stock - Tested and working - Supplied in our custom box for optimal protection. Functionality: Perfectly operational Cosmetic condition: Excellent – Markings optimally preserved, minimal signs of age. See photos for details. Special selection: Green Dot and Gray Dot, with low noise and microphonics verified using an Amplitrex AT-1000. Manufacturing code: Sylvania Electric Products Inc., USA – original marking on the base 288 / 513. 288 is the internal Sylvania code. 513 - 13th week of 1955 (March 1955). Discover why our tubes are different →